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  • Writer's pictureCaroline Cranshaw

Why Your Blood Type Matters When Trying To Lose Weight

Updated: Dec 7, 2020

Weight loss tends to be a formula that works for most when applied. Eat nutritious food that equals less calories than you burn. Simple, right? But more times than I can count, a client sits in my office week after week, claiming they are doing everything “right.” Some are only eating 1200-1500 calories a day and exercising three or more times a week. But the scale doesn't budge, and they have other persistent issues, such as arthritis, allergies, and other auto-immune disorders. What do you do then, when nothing else seems to work?

As a weight loss coach and hypnotherapist, I've tried countless diets over the years, and worked with thousands of people on every protocol under the sun. The eating plan I always seem to come back to is the blood type diet. If you don't know what your blood type is, an easy way to find out is to donate blood, or buy a home kit here. If you can’t seem to lose weight no matter what you do, it’s important to create a plan that addresses your individual needs, physically and mentally.

What Is The Blood Type Diet?

The Blood Type Diet was initially created in the 1960s by naturopathic physician James D'Adamo. It was further developed and made famous by his son, also a Naturopathic Doctor, Peter J. D'Adamo. The Blood Type Diet has been making headlines since Peter published his first book Eat Right for Your Type in 1996.

The concept behind the Blood Type Diet is that your body's reaction to food is directly connected to your blood type based on what your ancestors with the same blood type ate. The diet gives guidelines for each blood type—listing the foods that are beneficial to people with each blood type and the foods that may cause adverse reactions. The Japanese take blood types very seriously, using blood type to make decisions with hiring, dating and what type of diet to follow.

Blood Types and Health

Our blood type is important regarding our health because of three kinds of chemicals - antigens, antibodies, and lectins. An antigen is a chemical that produces an antibody by the immune system, in response to it. An antibody is a substance, made by cells of the immune system, to recognise foreign substances in the body and to attach to them. A lectin is usually a protein which can interact with antigens found on the blood cells, causing them to clump together or agglutinate.

There are four types of blood: O (40% of the population), A (30%), B (24%), AB (6%). Each type is identified by the presence of blood group antigens, which are sugars that lie on the surface of red blood cells. Those with A-type blood have A antigens, those with B-type blood have B antigens, and those with AB-type blood have both A and B antigens.

Type O is different because it does not have any antigens on its surface. An immune response is triggered in the body if blood is found with a different type of antigen and since type O red blood cells don't have antigens, no immune response is produced - making it the universal donor blood type.

Each blood type produces antibodies to other blood types. Blood-type A has antibodies against type B. Type B has antibodies against type A. Type AB, doesn't have antibodies towards type A or type B, and type O has antibodies against both type A and type B. Blood-type antibodies are incredibly potent and cause blood cells of the opposing type to clump in seconds.

What Peter D'Adamo found was that many foods caused the clumping of the cells of certain blood types but not of others. Some foods that may be beneficial to one blood type may be harmful to another. Many of the antigens in these foods have A or B-like characteristics. Therefore our immune system may try to attack what it perceives as a foreign substance.


Lectins are proteins, found in foods. Scientists believe that lectins are a form of defence in plants to keep insects away. Their characteristics can affect the blood as well as specific tissues, organs, and systems in the body. Many food lectins are similar to the blood-type antigens, which make that food harmful to other types.

For instance, milk has B-like characteristics. If a type O drinks milk, the immune system can react and try to reject it. Cells in the target area are clumped together and destroyed. Still, there's some protection from lectins as our immune system gets rid of 95% of the lectins in our food. The other 5% may cause issues if a particular blood type is reactive.

Lectins from particular foods, especially nightshade vegetables like tomatoes, peppers and potatoes, deposit in the joints after travelling through the bloodstream and end up attaching to the cells in the knees, hands and shoulders. Certain blood types can experience arthritis-like symptoms after eating these foods.

The body identifies the lectins in these areas as a threat and sends white blood cells in to destroy them. The white blood cells mistakenly end up damaging healthy tissue along with the problem lectins, causing pain and inflammation. If you want to learn more about the effects of lectins, I highly recommend the books by Dr. Stephen Gundry, Dr. Gundry’s Diet Evolution and The Plant Paradox.

How Blood Type Determines Microflora In Your Gut

Different blood types have distinct cultures of bacteria in their bodies. Specific bacteria are 50,000 times more likely to be detected in people with one blood type or another. These differing microbiomes have evolved from the changes to food supplies as humans migrated to different parts of the world. For example, the gut bacteria of people who descended from ancient agricultural populations whose diet was predominately plant-based carbs have evolved to metabolise carbohydrates more efficiently.

But in people who don't have this specific blood type capacity (like the descendants of hunter-gatherers whose gut bacteria is designed to digest animal protein), carb-based diets can cause issues. Inadequate digestion feeds harmful bacteria, which researchers have connected as an underlying cause of weight gain. Science is now proving that people prone to being overweight tend to have different bacteria in their gut than naturally slim people.

The Blood Type Diet is a way to reduce inflammation and optimise the beneficial bacteria, making it easier to lose weight.

Finnish researchers have recently proven that blood type antigens (sugar molecules on the surface of blood cells that determine blood type) act as a food source for microorganisms in the digestive tract. Various bacteria in your gut eat the sugars that comprise blood type antigens as a way of feeding themselves. Scientists are now able to change A and B blood types into O type blood by adding the bacteria that eat the blood type antigens.

So What Should Each Blood Type Eat?

O Blood Type

Type O has the highest levels of stomach acid, which greatly enhances their ability to metabolise the cholesterol in animal products and lowers their risk of heart disease and stroke with the strongest immune systems. However, Type O's are less able to metabolise simple carbohydrates, particularly from grains, which are more readily converted into fats and triglycerides. Many grains contain lectins that trigger the type O immune system, causing inflammation and auto-immune issues.

Things to Avoid: Type O’s should avoid most grains and items made with them, especially corn and wheat. Reduce or eliminate kidney and navy beans, lentils, brussels sprouts, cabbage, cauliflower, and mustard greens. O's thrive on intense aerobic exercises and activities.

A Blood Type

The A blood type thrives on a more plant-based diet and can metabolise carbohydrates more effectively than other types. People with this blood type to tend to have the lowest levels of stomach acid of all the types and may have trouble digesting animal protein and fat. They have higher rates of heart disease and cancer and are the least able to deal with stress. Focusing on fresh, organic foods, the Type A diet recommends more salmon, green veggies, pineapple and nuts.

Things to Avoid: Type A are very sensitive to the lectins in potatoes, sweet potatoes, yams, unfermented dairy, brazil nuts, cashews, chickpeas, wheat, cabbage, bananas, oranges, tomatoes, eggplant, mushrooms and peppers. Because of their lower stomach acid, they should avoid all red meat and pork and stick to chicken and fish.

B Blood Type

Type Bs thrive on an omnivore diet and metabolise animal products well, including dairy. Type Bs are predisposed to auto-immune disorders such as arthritis, diabetes (B+ has the highest risk), multiple sclerosis, and chronic fatigue syndrome and are more susceptible to viruses.

Type Bs need to avoid chicken. Chicken contains a lectin which triggers an immune response in B blood types which can lead to thickened blood and contribute to immune disorders. Fish is beneficial, but B's should limit shellfish, which contain lectins that can be harmful to their system.

The B Blood Type is reactive to chicken, shellfish and tomatoes and can gain weight when they eat corn, wheat, rye, buckwheat, lentils, peanuts and sesame seeds. These foods have lectins that impair the performance of the metabolic process, causing fatigue, fluid retention, and hypoglycaemia.

AB Blood Type

Having both A and B antigens cause AB's blood type to tend to be A-like with weak stomach acid, but more B-like with an innate ability to digest meat. Since type AB's have lower stomach acid than O or B blood types, it's helpful to supplement with digestive enzymes as well as limit portion size and frequency.

A recent study showed people with AB blood are 82 percent more likely to develop cognitive issues that may lead to dementia as they get older, so protecting brain health is very important. Like B blood types, the lectin in chicken irritates the blood and digestive tracts of AB's. While they should avoid beef, chicken, chickpeas and corn, people with the AB blood type can eat a variety of fish, lamb, turkey, dairy, and fresh produce.

If you would like a program that reprograms your mind to stop craving unhealthy food and eat less, check out my Virtual Gastric Band Program. What do you have to lose but the weight…

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